Containment, management, and disposal of various types of waste are long-standing problems. Early waste management and disposal systems were primitive, as there were few or no disposal or environmental regulations in place at the time. In countless instances, the waste was simply buried underground. The volume of waste that has been buried is tremendous. Some experts estimate that landfills in the United States alone hold more than 3 million cubic meters of buried waste. Further, much of the waste that was buried comprises heavy metals such as mercury and cadmium, carcinogenic materials such as trichloroethylene, radioactive materials, and other hazardous substances.
While burial and similar approaches produced an aesthetically pleasing result by removing the waste from sight, it was soon discovered that effluent from the buried waste was working its way through the soil and into the groundwater. This process is commonly known as leaching. Because groundwater is a major source of water for drinking and for agriculture, contamination of the groundwater by leaching is a major concern.
The contamination caused by buried waste is not limited solely to groundwater however. At least some of the contaminated groundwater finds its way into waterways such as streams, rivers, and lakes, thus polluting those waterways and poisoning the plant and animal life. Obviously, polluted waterways pose a threat to humans as well, particularly in the case of waterways and bodies of water used for recreational purposes and/or as a source of drinking water.
Not all of the cases of groundwater pollution arise from the leaching of chemicals from waste sources. In some cases, the waste is buried in the path of the groundwater, and as groundwater flows through the waste, it collects various chemicals and toxins from the waste and deposits those chemicals and toxins in other soils and waterways.
While many of the problems associated with buried waste concern the effect of leachate on groundwater, buried waste also typically emits gas phase contaminants that must likewise be contained and managed. Such gas phase contaminants can also pollute the soil and the groundwater, and may build up to unsafe pressures which could ultimately result in explosion and/or atmospheric venting of the gas.
Clean soil and groundwater are important to human, plant, and animal life as well as to the environment in general. Accordingly, a variety of methods and devices have been devised to attempt to resolve the problems induced by buried waste. These remedies can be broadly grouped into the categories of remediation and containment. Remediation remedies focus on processes designed to change the chemical composition of a contaminated material or contaminant to one more benign, while containment remedies seek to eliminate the pollution problem by treating or isolating the contaminants and contaminated material from the surrounding area.
Traditional remediation approaches have involved removing the contaminated material. This may then be incinerated, treated with chemical or biological processes, or other treatment processes. Often contaminated materials are simply removed from one location and relocated for storage at another location. Such approaches are problematic for a variety of reasons. In particular, many of these remediation techniques are expensive and potentially hazardous. Further, it is difficult to verify the effectiveness of many of the treatments and remediation-type approaches may not be appropriate for all types of contaminated material. Finally, determining the proper remediation technique is, in itself, a complex and time-consuming process, particularly in view of the web of regulations and procedures that govern such treatments.
Some approaches to remediation are conducted on-site and attempt to resolve problems of removal and transportation. These techniques typically employ the placement of delivery wells into a site, through which a treatment process is applied. Withdrawal wells may also be used to create a flow across contaminated soil. Problems with such on-site remediation processes can lead to the exposure of the surrounding environment to the contaminants. Withdrawal wells and delivery wells may be strategically placed to reduce this problem, but do not provide containment.
U.S. Pat. No. 5,054,961 to Sherman, issued Oct. 8, 1991, the disclosure of which is incorporated herein by reference, discusses an alternate method of on-site treatment. This method uses an underground barrier to direct the flow of ground water, creating a “bottomless tank.” A gradient of pollutants and water is formed by the directed flow allowing for directed treatment. While such a treatment scheme allows for on-site treatment, it could not provide complete containment and may allow contaminants to escape into the surrounding regions.
Containment, barrier, or in situ approaches are problematic as well. One known containment approach is simply to dig up and remove the contaminated soil for treatment and/or disposal. This approach, also referred to generally as treatment, is expensive and time-consuming and often accomplishes little more than moving the problem to another location, which with certain contaminants can be a rather hazardous activity. Other containment approaches involve installing vertical and/or horizontal barriers around the buried waste. In theory, this approach is attractive because it does not involve digging up or otherwise disturbing the buried waste.
However, conventional containment or barrier systems suffer from a variety of inadequacies including lack of durability, continuity and integrity. These inadequacies are a function of numerous factors associated with the environment in which the containment or barrier systems are located including, but not limited to: exposure to harsh chemicals such as concentrated saline solutions, and saturated calcite and gypsum solutions; exposure to extreme thermal gradients such as are typically experienced in freeze/thaw zones; and exposure to stresses induced by shifting in the earth.
Hydraulic conductivity, which is the rate at which a fluid or hazardous substance flows through a barrier, is unacceptably high in some barrier systems while other conventional barrier systems are not particularly well-suited to a variety of soil conditions such as hard rock and sand. A further flaw is that many barrier systems do not provide methods for evaluating the integrity of the barrier during and after installation, which is complicated by the fact that many barrier systems also lack provision for long term monitoring of the containment zone and any leachate therefrom. The inability to monitor a barrier system that is isolating hazardous waste is unacceptable because of the potential harm that can be caused to the surrounding environment. The lack of durability, continuity and integrity in known containment systems has a significant detrimental effect on the performance of those systems and the effectiveness of those containment and barrier systems cannot be readily determined or evaluated.
Accordingly, what is needed are improved in situ containment systems and methods and processes for treating contaminants contained within such a system. Methods or processes for treating a contaminant or removing a desired material from a zone of interest, on-site, while containing the zone of interest and any effluent therefrom would be advantageous.